Functional assays of local connectivity in the somatosensory cortex of individuals with autism.

Emerging evidence for differences between individuals with autism spectrum disorder (ASD) and neurotypical (NT) individuals in somatic processing and brain response to touch suggests somatosensory cortex as a promising substrate for elucidating differences in functional brain connectivity between individuals with and without autism. Signals from adjacent digits project to neighboring locations or representations in somatosensory cortex. When a digit is stimulated, i.e. touched, its representation in cortex is directly activated; local intracortical connections indirectly activate nonprimary cortical representations corresponding to adjacent digits. The response of the nonprimary cortical representations is thus a proxy for connection strength. Local overconnectivity in autism implies that the nonprimary/primary response ratios of the ASD group will be higher than those of the NT group. D1 and D2 of the dominant hand of the participant were individually stimulated while we recorded neural responses using magnetoencephalography. The cortical representations of D1 and D2 (somatosensory-evoked fields) were computed from the ensemble-averaged data using (a) dipole model fits and (b) singular value decomposition. Individual adjacent/primary response ratios were measured, and group response ratio data were fitted with straight lines. Local overconnectivity in autism implies steeper ASD vs. NT group slopes. Our findings did not support local overconnectivity. Slopes were found to be significantly shallower for the ASD group than the NT group. Our findings support the idea of local underconnectivity in the somatosensory cortex of the brains of individuals with ASD.

Increased response variability in autistic brains?

One of the key ideas regarding atypical connectivity in autistic brains is the hypothesis of noisier networks. The systems level version of this hypothesis predicts reduced reliability or increased variability in the evoked responses of individuals with autism. Using magnetoencephalography, we examined the response of individuals with autism spectrum disorder versus matched typically developing persons to passive tactile stimulation of the thumb and index finger of the dominant (right) hand. A number of different analyses failed to show higher variability in the evoked response to the thumb or to the index finger in the autism group as compared with typicals. Our results argue against the hypothesis that the brain networks in autism are noisier than normal.

How somatic cortical maps differ in autistic and typical brains.

The comorbidity of 'core characteristics' and sensorimotor abnormalities in autism implies abnormalities in brain development of a general and pervasive nature and atypical organization of sensory cortex. By using magnetoencephalography, we examined the cortical response to passive tactile stimulation of the thumb and index finger of the dominant hand and lip of the individuals with autism spectrum disorder and typically developing persons. The distance between the cortical representations of thumb and the lip was significantly larger in the autism group than in typicals. Moreover, in cortex, the thumb is typically closer to the lip than the index finger. This was not observed in persons with autism. Our findings are arguably the first demonstration of abnormality in sensory organization in the brains of persons with autism.